U.S. patent number 5,869,552 [Application Number 08/900,816] was granted by the patent office on 1999-02-09 for water-dispersible polymer and coating composition containing the same.
This patent grant is currently assigned to The Dexter Corporation. Invention is credited to Walter R. Pedersen, Joseph Devasia Ponmankal.
United States Patent |
5,869,552 |
Pedersen , et al. |
February 9, 1999 |
Water-dispersible polymer and coating composition containing the
same
Abstract
A water-dispersible polymer and a coating composition containing
the water-dispersible polymer are disclosed. The water-dispersible
polymer is prepared from: (a) an epoxy compound having about two
epoxy groups, such as an epoxy resin, (b) a linking compound having
(i) conjugated carbon-carbon double bonds or a carbon-carbon triple
bond and (ii) a moiety capable of reacting with an epoxy group,
such as sorbic acid, and (c) acrylic monomers, at least a portion
of which are capable of rendering the polymer water dispersible,
such as acrylic acid, wherein the epoxy portion (a) of the polymer
is covalently linked to the polymerized acrylic portion (c) by
linking compound (b). The coating composition contains the
water-dispersible polymer, a fugitive base to solubilize the
polymer, a curing agent, and a carrier containing water.
Inventors: |
Pedersen; Walter R. (Chicago,
IL), Ponmankal; Joseph Devasia (Chicago, IL) |
Assignee: |
The Dexter Corporation (Windsor
Locks, CT)
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Family
ID: |
24417327 |
Appl.
No.: |
08/900,816 |
Filed: |
July 25, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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603885 |
Feb 22, 1996 |
5830952 |
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Current U.S.
Class: |
523/413;
427/388.4; 523/407; 523/408; 523/412; 428/418 |
Current CPC
Class: |
C08F
290/144 (20130101); C08F 283/10 (20130101); C09D
151/08 (20130101); Y10T 428/31529 (20150401) |
Current International
Class: |
C09D
151/08 (20060101); C08F 283/10 (20060101); C08F
290/00 (20060101); C08F 290/14 (20060101); C08F
283/00 (20060101); C08K 003/20 (); C08L
063/02 () |
Field of
Search: |
;523/413,407,408,412
;428/418 ;427/388.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 469 646 A1 |
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Feb 1992 |
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EP |
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1720922 |
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Jan 1968 |
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DE |
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1 720 922 |
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Jan 1968 |
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DE |
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WO 92/14763 |
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Sep 1992 |
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WO |
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Other References
JT.K. Woo et al., "Synthesis and Characterization of
Water-Reducible Graft Epoxy Copolymers," J. Coat. Tech., 54 (689)
(1982), pp. 41-55. .
R.N. Johnson et al., "Water-Borne Phenoxy Resins Low VOC Coatings
with Excellent Toughness, Flexibility and Adhesion," Water-Borne
and Higher-Solids Coating Symposium, Feb. 3-5, 1988, New Orleans,
LA, pp. 443-461..
|
Primary Examiner: Marquis; Melvyn
Assistant Examiner: Aylward; D.
Attorney, Agent or Firm: Marshall, O'Toole, Gerstein, Murray
& Borun
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of U.S. patent application Ser.
No. 08/603,885, filed Feb. 22, 1996, now U.S. Pat. No. 5,830,952.
Claims
What is claimed is:
1. A water-dispersible polymer having the structure
wherein E is an epoxy portion of the polymer having at least one
epoxy group, A is a polymerized acrylic portion of the polymer, and
L is a linking portion of the polymer which covalently links E to
A, said polymer prepared from
(a) an epoxy compound having about two epoxy groups;
(b) a linking compound having
(i) either conjugated carbon-carbon double bonds or a carbon-carbon
triple bond, and
(ii) a moiety capable of reacting with an epoxy group, said linking
compound present in an amount of about 0.003% to about 2.5% by
weight of the polymer and in an amount sufficient to react with at
least 1% and up to about 50% of the epoxy groups provided by the
epoxy compound; and
(c) acrylic monomers, at least a portion of which are selected from
the group consisting of an .alpha.,.beta.-unsaturated carboxylic
acid, acrylamide methacrylamide and mixtures thereof, to render the
polymer water dispersible;
wherein the epoxy group of epoxy portion E is opened with water,
ammonia, a primary amine, a secondary amine, an alcohol, a diol, a
phenol, an alkanolamine, phosphoric acid, a phosphoric acid
monoester, a phosphoric acid diester, or a mixture thereof.
2. The polymer of claim 1 comprising about 5% to about 95% by
weight of the epoxy portion E.
3. The polymer of claim 1 wherein the epoxy compound has an epoxy
equivalent weight of about 180 to about 20,000.
4. The polymer of claim 1 wherein the epoxy compound comprises a
polyether diepoxide prepared in a reaction between a bisphenol and
a compound having about two epoxy groups.
5. The polymer of claim 1 wherein the linking compound contains
conjugated carbon-carbon double bonds.
6. The polymer of claim 1 wherein the linking compound contains a
carbon-carbon triple bond.
7. The polymer of claim 1 wherein the linking compound has the
structure ##STR13## wherein R.sub.1 is selected from the group
consisting of hydrogen, phenyl, C.sub.1 -C.sub.10
alkoxy-substituted phenyl, halo-substituted phenyl, C.sub.1
-C.sub.18 alkyl-substituted phenyl, C.sub.1 -C.sub.18 alkyl,
C.sub.5 -C.sub.7 cycloalkyl, phenyl-substituted C.sub.1 -C.sub.18
alkyl, phenyl-substituted C.sub.5 -C.sub.7 cycloalkyl,
halo-substituted C.sub.1 -C.sub.18 alkyl, halo-substituted C.sub.5
-C.sub.7 cycloalkyl, unsaturated C.sub.1 -C.sub.18 aliphatic
hydrocarbyl, and unsaturated C.sub.5 -C.sub.7 cycloaliphatic
hydrocarbyl; r is a numeral from 1 to 6; s is a numeral from 0 to
6; p is a numeral from 0 to 18; and Y is a moiety capable of
reacting with an epoxy group.
8. The polymer of claim 7 wherein the Y group is selected from the
group consisting of a carboxylic acid group; a hydroxyl group; an
amino group --N(R.sub.2).sub.2 ; an amido group
--CON(R.sub.2).sub.2, wherein R.sub.2, independently, are hydrogen,
C.sub.1 -C.sub.4 alkyl, or phenyl; and a mercapto group --SR.sub.3,
wherein R.sub.3 is hydrogen, C.sub.1 -C.sub.4 alkyl, or phenyl.
9. The polymer of claim 1 wherein the linking compound is selected
from the group consisting of sorbic acid, sorbic alcohol, a
dicyclopentadiene acids, a conjugated unsaturated fatty acid,
eleostearic acid, 3-pentyn-1-ol, 2-pentyn-1-ol, 4-pentynoic acid,
4-pentyn-1-ol, 4-pentyn-2-ol, 1-pentyn-3-ol,
heptacose-10,12-diynoic acid, heptadeca-2,4-diynoic acid,
heneicosa-2,4-diynoic acid, 2-heptynoic acid, 2-hexynoic acid,
nonacosa-10,12-diynoic acid, nonadeca-1,4-diynoic acid, 2-nonynoic
acid, pentadeca-2,4-diynoic acid, pentacosa-10,12-diynoic acid,
phenyl-propiolic acid, propiolic acid, tetrolic acid,
tricosa-10,12-diynoic acid, 10-undecynoic acid, 1-butyn-3-ol,
2-butyn-1-ol, 3-butyn-1-ol, 2-decyn-1-ol, 3-decyn-1-ol,
3,6-dimethyl-1-heptyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol,
3,4-dimethyl-1-pentyn-3-ol, 3-ethyl-1-heptyn-3-ol,
4-ethyl-1-hexyn-3-ol, 3-ethyl-5-methyl-1-heptyn-3-ol,
4-ethyl-1-octyn-3-ol, 3-ethyl-1-pentyn-3-ol,
1-ethynyl-1-cyclohexanol, 1-heptyn-3-ol, 2-heptyn-1-ol,
3-heptyn-1-ol, 4-heptyn-2-ol, 5-heptyn-3-ol, 1-hexyn-3-ol,
2-hexyn-1-ol, 3-hexyn-1-ol, 4-hexyn-2-ol, 5-hexyn-1-ol,
5-hexyn-3-ol, 3-methyl-1-butyn-3-ol, 5-methyl-1-hexyn-3-ol,
3-methyl-1-pentyn-3-ol, 3-nonyn-1-ol, 1-octyn-3-ol, 3-octyn-1-ol,
1-phenyl-2-propyn-1-ol, 2-propyn-1-ol, 10-undecyn-1-ol,
3-aminophenyl-acetylene, propargylamine, and mixtures thereof.
10. The polymer of claim 1 wherein the linking compound has a
maximum of twelve carbon atoms.
11. The polymer of claim 1 wherein the polymerized acrylic portion
A comprises at least 5%, by weight, of monomers capable of
rendering the polymer water dispersible.
12. The polymer of claim 1 comprising about 0.25% to about 20%, by
weight of the polymer, of monomers capable of rendering the polymer
water dispersible.
13. The polymer of claim 1 wherein the .alpha.,.beta.-unsaturated
carboxylic acid is selected from the group consisting of acrylic
acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid,
mesaconic acid, citraconic acid, sorbic acid, fumaric acid, and
mixtures thereof.
14. The polymer of claim 1 wherein the polymerized acrylic portion
A comprises 0% to about 95% of a vinyl monomer, an ester of an
.alpha.,.beta.-unsaturated acid, an acrylonitrile, or a mixture
thereof.
15. The polymer of claim 14 wherein the polymerized acrylic portion
A comprises a monomer selected from the group consisting of
styrene; a halostyrene; isoprene; a conjugated butadiene;
.alpha.-methylstyrene; vinyl toluene; vinyl naphthalene; methyl
acrylate; ethyl acrylate; propyl acrylate; isopropyl acrylate;
butyl acrylate; isobutyl acrylate; pentyl acrylate; isoamyl
acrylate; hexyl acrylate; ethylhexyl acrylate; lauryl acrylate; a
C.sub.4 -C.sub.12 alkyl acrylate; a C.sub.1 -C.sub.12 alkyl
methacrylate; a C.sub.1 -C.sub.12 alkyl crotonate; dimethyl
maleate; dibutyl fumarate; vinyl chloride; acrylonitrile;
methacrylonitrile; vinyl acetate; vinyl propionate; vinyl stearate;
and mixtures thereof.
16. The polymer of claim 1 wherein the epoxy portion E has the
structure ##STR14## wherein t is 0 to about 70; the linking portion
L comprises sorbic acid; and the polymerized acrylic portion A is
predominantly acrylic acid, methacrylic acid, or a mixture
thereof.
17. The polymer of claim 16 wherein the polymerized acrylic portion
A further comprises a monomer selected from the group consisting of
styrene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl
methacrylate, and mixtures thereof.
18. A water-dispersible polymer prepared by a method
comprising:
(a) reacting (i) an epoxy compound having about two epoxy groups
with (ii) a sufficient amount of a linking compound to consume at
least 1% and up to about 50% of epoxy groups provided by the epoxy
compound, said linking compound present in an amount of about
0.003% to about 2.5% by weight of the polymer, and having
(A) either conjugated carbon-carbon double bonds or a carbon-carbon
triple bond, and
(B) a moiety capable of reacting with an epoxy group,
to provide a modified epoxy compound having at least one epoxy
group and wherein the linking compound is covalently bonded to the
epoxy compound;
(b) hydrolyzing the epoxy group of the modified epoxy compound of
step (a) to provide an .alpha.-glycol at a terminal end of the
modified epoxy compound; and
(c) reacting the hydrolyzed epoxy compound of step (b) with (iii) a
sufficient amount of acrylic monomer selected from the group
consisting of an .alpha.,.beta.-unsaturated carboxylic acid,
acrylamide, methacrylamide and mixtures thereof, such that the
acrylic monomer copolymerizes with the conjugated carbon-carbon
double bonds or the carbon-carbon triple bond of the linking
compound to provide the water-dispersible polymer.
19. The water-dispersible polymer of claim 18 wherein step (b) of
the method comprises ring opening the epoxy group of the modified
epoxy compound after step (a) with a nitrogen compound having the
structure (R.sub.4).sub.2 NH, wherein the R.sub.4 groups are,
independently, hydrogen, an alkyl group having one to six carbon
atoms, phenyl, or a hydroxyalkyl group having one to six carbon
atoms, to provide an .alpha.-aminoalcohol at a terminal end of the
modified epoxy compound.
20. The water-dispersible polymer of claim 18 wherein step (b) of
the method comprises ring opening the epoxy group of the modified
epoxy compound after step (a) with a hydroxyl-containing compound
having the structure R.sub.5 OH, wherein the R.sub.5 group is
hydrogen, an alkyl group having one to six carbon atoms, phenyl, or
a hydroxyalkyl group having one to six carbon atoms, to provide an
.alpha.-hydroxy ether at a terminal end of the modified epoxy
compound.
21. The water-dispersible polymer of claim 18 wherein step (b) of
the method comprises ring opening the epoxy group of the modified
epoxy compound after step (a) with a phosphoric acid having the
structure ##STR15## wherein the R.sub.6 groups are, independently,
hydrogen, an alkyl group having one to six carbon atoms, or phenyl,
to provide an .alpha.-hydroxy phosphate ester at a terminal end of
the modified epoxy compound.
22. A coating composition comprising:
(a) about 5% to about 60%, by weight of non-volatile material, of a
water-dispersible polymer having the structure
wherein E is an epoxy portion of the polymer, said epoxy portion E
derived from an epoxy compound having about two epoxy groups; L is
a linking portion of the polymer, said linking portion L derived
from a linking compound having
(A) either conjugated carbon-carbon double bonds or a carbon-carbon
triple bond, and
(B) a moiety capable of reacting with an epoxy group, said linking
compound present in an amount of about 0.003% to about 2.5% by
weight of the polymer and in an amount sufficient to react with at
least 1% and up to about 50% of epoxy groups provided by the epoxy
compound;
and A is a polymerized acrylic portion of the polymer, said acrylic
portion A comprising polymerized acrylic monomers, at least a
portion of said monomers selected from the group consisting of an
.alpha.,.beta.-unsaturated carboxylic acid, acrylamide, and
methacrylamide, to render the polymer water dispersible, wherein
the epoxy portion E of the polymer is covalently linked to the
acrylic portion A by the linking portion L and wherein the epoxy
group of epoxy portion E is opened with water, ammonia, a primary
amine, a secondary amine, an alcohol, a diol, a phenol, an
alkanolamine, phosphoric acid, a phosphoric acid monoester, a
phosphoric acid diester, or a mixture thereof;
(b) a sufficient amount of a fugitive base to disperse the
water-dispersible polymer in water;
(c) about 0.5% to about 25%, by weight of nonvolatile material, or
a curing agent; and
(d) a carrier comprising water and a volatile organic solvent.
23. The composition of claim 22 wherein the polymerized acrylic
portion A comprises an .alpha.,.beta.-unsaturated acid, and wherein
a sufficient amount of the fugitive base is present to neutralize
about 20% to about 100% of carboxylic acid groups present in the
acrylic portion A of the polymer.
24. The composition of claim 22 wherein the fugitive base is
selected from the group consisting of a primary amine, a secondary
amine, a tertiary amine, a primary alkanolamine, a secondary
alkanolamine, a tertiary alkanolamine, ammonium hydroxide, an
alkylammonium hydroxide, and mixtures thereof, wherein the alkyl
groups of the amines, alkanolamines and alkylammonium hydroxides
have one to about four carbon atoms.
25. The composition of claim 22 wherein the fugitive base is
selected from the group consisting of ammonium hydroxide, a
tetraalkylammonium hydroxide wherein an alkyl group has one to
about 4 carbon atoms, tetramethylammonium hydroxide,
monoethanolamine, dimethylamine, methyldiethanolamine, benzylamine,
diisopropylamine, methylethanolamine, butylamine, piperazine,
dimethylethanolamine, diethylethanolamine, diethanolamine,
morpholine, N-methylmorpholine, N-ethylmorpholine, triethylamine,
2-dimethylamine-2-methyl-1-propanol, diisopropanolamine,
trimethylamine, N-methylpiperidine, 2-amino-2-methyl-1-propanol,
piperidine, pyridine, dimethylaniline, and mixtures thereof.
26. The composition of claim 22 wherein the curing agent is
selected from the group consisting of a phenolic resin, an
aminoplast, a carbodiimide, and mixtures thereof.
27. A method of coating a metal substrate comprising:
(i) applying a coating composition of claim 22 to at least one
surface of the metal substrate; and
(ii) heating the metal substrate having the coating composition
applied thereon for a sufficient time and at a sufficient
temperature to remove the fugitive base and the carrier from the
composition and provide a crosslinked cured coating
composition.
28. The method of claim 27 wherein the metal substrate having the
coating composition applied thereon is heated for about 6 seconds
to about 15 minutes at a temperature of about 350.degree. F. to
about 500.degree. F.
29. A metal article having at least one surface thereof coated with
an adherent layer of a cured coating composition of claim 22.
30. The polymer of claim 1 wherein the linking compound L is sorbic
acid, and the polymerized acrylic portion A is prepared from
acrylic monomers selected from the group consisting of acrylic
acid, methacrylic acid, styrene, ethyl acrylate, and methyl
methacrylate.
Description
FIELD OF THE INVENTION
The present invention relates to water-dispersible polymers and to
coating compositions for metal substrates containing the
water-dispersible polymers. The coating composition comprises a
water-dispersible polymer, a fugitive base, a curing agent, and a
carrier comprising water and a volatile organic solvent. The
water-dispersible polymer is prepared from: (a) an epoxy compound
having about two epoxy groups, (b) a linking compound having (i)
conjugated carbon-carbon double bonds or a carbon-carbon triple
bond and (ii) a moiety capable of reacting with an epoxy group, and
(c) acrylic monomers, wherein the epoxy portion (a) of the polymer
is covalently linked to the polymerized acrylic portion (c) by the
linking compound (b).
BACKGROUND OF THE INVENTION
It is well known that an aqueous solution in contact with an
untreated metal substrate can result in corrosion of the untreated
metal substrate. Therefore, a metal article, such as a metal
container for a water-based product, like a food or beverage, is
rendered corrosion resistant in order to retard or eliminate
interactions between the water-based product and the metal article.
Conventionally, corrosion resistance is imparted to the metal
article, or to a metal substrate in general, by passivating the
metal substrate, or by coating the metal substrate with a
corrosion-inhibiting coating.
Investigators continually have sought improved coating compositions
that reduce or eliminate corrosion of a metal article and that do
not adversely affect an aqueous product packaged in the metal
article. For example, investigators have sought to improve the
imperviousness of the coating in order to prevent corrosion-causing
ions, oxygen molecules, and water molecules from contacting and
interacting with a metal substrate. Imperviousness can be improved
by providing a thicker, more flexible and more adhesive coating,
but often, improving one particular advantageous coating feature is
achieved at the expense of another advantageous coating
feature.
In addition, practical considerations limit the thickness, adhesive
properties and flexibility of a coating applied to a metal
substrate. For example, thick coatings are expensive, require a
longer cure time, can be esthetically unpleasing, and can adversely
affect the process of stamping and molding the coated metal
substrate into a useful metal article. Similarly, the coating
should be sufficiently flexible such that the continuity of the
coating is not destroyed during stamping and molding of the metal
substrate into the desired shape of the metal article.
Investigators also have sought coatings that possess chemical
resistance in addition to corrosion inhibition. A useful coating
for the interior of a metal container must be able to withstand the
solvating properties of a product packaged in the metal container.
If the coating does not possess sufficient chemical resistance,
components of the coating can be extracted into the packaged
product and adversely affect the product. Even small amounts of
extracted coating components can adversely affect sensitive
products, like beer, by imparting an off-taste to the product.
Conventionally, organic solvent-based coating compositions were
used to provide cured coatings having excellent chemical
resistance. Such solvent-based compositions include ingredients
that are inherently water insoluble, and thereby effectively resist
the solvating properties of water-based products packaged in the
metal container. However, because of environmental and
toxicological concerns, and in order to comply with increasingly
strict governmental regulations, an increasing number of coating
compositions are water based. The water-based coating compositions
include ingredients that are water soluble or water dispersible,
and, therefore, cured coatings resulting from water-based coating
compositions often are more susceptible to the solvating properties
of water.
Epoxy-based coatings and polyvinyl chloride-based coatings have
been used to coat the interior of metal containers for foods and
beverages because these coatings exhibit an acceptable combination
of adhesion to a metal substrate, flexibility, chemical resistance,
and corrosion inhibition. However, epoxy-based coatings and
polyvinyl chloride-based coatings have serious disadvantages that
investigators still are attempting to overcome.
For example, coatings based on polyvinyl chloride or related
halide-containing vinyl polymers, like polyvinylidene chloride,
possess the above-listed advantageous properties of chemical
resistance and corrosion inhibition, and are economical. However,
curing a polyvinyl chloride or related halide-containing vinyl
polymer can generate toxic monomers, such as vinyl chloride, a
known carcinogen. In addition, the disposal of a halide-containing
vinyl polymer, such as by incineration, also can generate toxic
monomers. The generated vinyl chloride thereby poses a potential
danger to workers in metal can manufacturing plants, in food
processing and packaging plants, and at disposal sites. Disposal of
polyvinyl chloride and related polymers also can produce
carcinogenic dioxins and environmentally harmful hydrochloric acid.
Government regulators, therefore, are acting to eliminate the use
of polyvinyl chloride-based coating compositions that contact food,
and thereby eliminate the environmental and health concerns
associated with halide-containing vinyl polymers.
To overcome these environmental concerns, epoxy-based coating
compositions recently have been used to coat the interior of food
and beverage containers. However, epoxy-based coatings also possess
disadvantages. For example, epoxy-based coating compositions are
more expensive than polyvinyl chloride-based coating
compositions.
Various patents disclose waterborne coating compositions for metal
cans. In general, prior patents disclose coating compositions
including water-borne thermoset resins for use as can coatings. The
thermoset resins can be formulated with a crosslinking agent to
provide crosslinked films during cure, as demonstrated by the
resistance of the cured coating to the effects of organic solvents
such as methyl ethyl ketone. The cured thermoset resins often do
not have sufficient flexibility for use as can coatings.
Recently, waterborne phenoxy resins were disclosed as useful in
coatings for metal cans. These waterborne phenoxy resins are high
molecular weight thermoplastic resins that are difficult to process
and are too expensive for practical commercial use. In addition,
because these phenoxy resins are thermoplastic resins, cured
coatings derived therefrom are not resistant to organic solvents,
although the cured coatings often provide sufficient barrier
properties to water-based compositions for use as can coatings.
Investigators, therefore, have sought a waterborne coating
composition for the interior of food and beverage containers that
retains the advantageous properties of adhesion, flexibility,
chemical resistance and corrosion inhibition, and that is
economical and does not adversely affect the food and beverages
packaged in the container.
Investigators prefer a thermosetting coating composition because
such compositions are easier to handle and provide better chemical
resistance than thermoplastic coating compositions. A thermosetting
coating composition also requires a crosslinking agent, generally a
phenolic resin, an aminoplast, or a similar resin, in order to
provide a cured coating having a sufficient molecular weight.
Prior investigators have studied waterborne epoxy resin-based
compositions for application to metal substrates. Many of these
investigators sought epoxy resin-based aqueous compositions that
provide a sufficiently flexible cured coating such that the coated
metal substrate can be deformed without destroying film continuity.
Often, conventional epoxy resins provide a rigid cured film thereby
making it difficult to impossible to coat the metal substrate prior
to deforming, i.e., shaping, the metal substrate into a metal
article, like a metal can. Coating a metal substrate prior to
shaping the metal substrate is a standard industrial practice.
For example, Johnson et al. U.S. Pat. No. 4,954,553 discloses an
aqueous coating composition comprising a carboxyl-bearing phenoxy
resin and a resin that is soft in comparison to the phenoxy resin,
like a polyester. The carboxyl-bearing phenoxy resin is prepared by
grafting ethylenically unsaturated monomers to the phenoxy resin.
The coating composition provides flexible cured coatings. Fan U.S.
Pat. Nos. 4,355,122 and 4,374,875 disclose a water-borne phenolic
composition wherein an ethylenically unsaturated monomer including
a carboxyl group is grafted onto a phenoxy resin by standard free
radical polymerization techniques, then the carboxyl groups are
neutralized by a base.
Chu et al. U.S. Pat. No. 4,446,258 discloses an aqueous coating
composition comprising: (1) the neutralized reaction product of an
epoxy resin with a preformed addition polymer containing carboxyl
groups, and (2) an acrylic or vinyl polymer, which is prepared
either in situ or added to the composition, and which is different
from the preformed addition polymer.
Evans et al. U.S. Pat. No. 4,212,781 discloses grafting an acrylic
monomer or monomer blend to an epoxy resin to provide a polymeric
blend including unreacted epoxy resin, an acrylic resin and a graft
polymer of the acrylic resin and epoxy resin. Steinmetz U.S. Pat.
No. 4,302,373 discloses a waterborne coating composition consisting
essentially of the neutralized reaction product of a modified
polyepoxide (e.g., an ester or ether) or a phenolic and a
carboxyl-functional polymer.
Patel U.S. Pat. No. 4,963,602 discloses aqueous coating
compositions including an epoxy resin, an acrylic resin, a phenoxy
resin, a novolac resin, and a resol resin. Wu U.S. Pat. Nos.
3,943,187 and 3,997,694 disclose an organic solvent-based coating
composition consisting essentially of a blend of an acrylic polymer
having hard and soft segments and an epoxy resin. Salensky U.S.
Pat. No. 4,638,038 discloses modified phenoxy resins wherein
anhydrides or polycarboxylic acids are grafted onto a phenoxy
resin. Spencer U.S. Pat. No. 5,296,525 discloses (a) the reaction
product of an epoxy resin with a monomer having unsaturated groups,
(b) wherein the reaction product of (a) then is reacted with a
preformed carboxyl-functional polymer and a tertiary amine, (c)
followed by reacting the reaction product of (b) with unsaturated
monomers in an emulsion polymerization.
Other patents that disclose epoxy resins admixed with acrylic
resins, or having acrylic resins grafted thereon, include Matthews
et al. U.S. Pat. No. 4,247,439; Evans et al. U.S. Pat. No.
4,308,185; Wu U.S. Pat. No. 4,021,396; McCarty U.S. Pat. No.
4,444,923; Brown et al. U.S. Pat. No. 4,585,813; and Ting et al.
U.S. Pat. No. 4,480,058.
Publications disclosing a water-based coating compositions
including an epoxy resin and an acrylic resin include:
J. T. K. Woo et al., "Synthesis and Characterization of
Water-Reducible Graft Epoxy Copolymers," J. Coat. Tech., 54 (1982),
pp. 41-55; and
R. N. Johnson et al., "Water-Borne Phenoxy Resins Low VOC Coatings
with Excellent Toughness, Flexibility and Adhesion," presented at
the Water-Borne and Higher-Solid Coatings Symposium, Feb. 3-5, 1988
in New Orleans, La.
The above-identified patents and publications disclose waterborne
coating compositions comprising an epoxy resin and an acrylic
resin. The patents and publications do not disclose a waterborne
coating composition comprising a water-dispersible polymer
comprising an epoxy resin covalently linked to an acrylic resin by
a linking compound having conjugated carbon-carbon double bonds or
a triple bond.
The present coating compositions, after curing, demonstrate: (1)
excellent flexibility; (2) excellent adhesion; and (3) excellent
chemical resistance and corrosion inhibition.
SUMMARY OF THE INVENTION
The present invention is directed to waterborne coating
compositions that, after curing, effectively inhibit corrosion of a
metal substrate; do not adversely affect products packaged in a
container having an interior surface coated with the cured
composition; and exhibit excellent flexibility, chemical resistance
and adhesion. The coating compositions effectively inhibit
corrosion of ferrous and nonferrous metal substrates when the
composition is applied to a surface of the metal substrate, then
cured for a sufficient time and at a sufficient temperature to
provide a crosslinked coating. A coating composition of the present
invention can be used both on the interior and exterior of can ends
and can bodies, and on metal closures for food containers.
A present coating composition overcomes disadvantages associated
with prior epoxy resin-based compositions and comprises:
(a) a water-dispersible polymer prepared from
(i) an epoxy compound having about two epoxy groups, like an epoxy
resin;
(ii) a linking compound having
(A) either conjugated carbon-carbon double bonds or a carbon-carbon
triple bond, and
(B) a moiety capable of reacting with an epoxy group; and
(iii) acrylic monomers, at least a portion of which are capable of
rendering the polymer water dispersible, wherein the polymer has at
least one epoxy group and the epoxy portion (i) of the polymer is
covalently linked to the polymerized acrylic portion (iii) by
linking compound (ii);
(b) a fugitive base, like a tertiary amine;
(c) a curing agent; and
(d) a carrier comprising water and a volatile organic solvent.
In particular, the present coating compositions comprise:
(a) about 5% to about 60%, by weight of nonvolatile material, of a
water-dispersible polymer;
(b) a sufficient amount of a fugitive base to render the
water-dispersible polymer water dispersible; and
(c) about 0.5% to about 25%, by weight of nonvolatile material, of
a curing agent, like a phenolic resin or an aminoplast.
The water-dispersible polymer incorporated into the coating
composition is prepared from (i) an epoxy compound, (ii) a linking
compound having an activated unsaturated carbon-carbon bond moiety
and a moiety capable of reacting with an epoxy group, and (ii)
acrylic monomers, at least some of which are capable of rendering
the polymer water dispersible. As used here and throughout the
specification, the term "an activated unsaturated carbon-carbon
bond moiety" is defined as either conjugated carbon-carbon double
bonds or a carbon-carbon triple bond.
The epoxy compound has about two epoxy groups, i.e., about 1.5 to
about 2.5 epoxy groups per molecule of epoxy compound, and an epoxy
equivalent weight (EEW) of about 180 to about 20,000, and is
present in an amount of about 5% to about 95% by weight of the
polymer. The linking compound having an activated unsaturated
carbon-carbon bond moiety and a moiety capable of reacting with an
epoxy group is present in a sufficient amount to react with at
least about 1% (i.e., about 1% or more) and up to about 50% of the
epoxy groups provided by the epoxy compound. Alternatively stated,
the linking compound is present in an amount of about 0.1% to about
5% by weight of the epoxy compound, or about 0.003% to about 4% by
weight of the water-dispersible polymer.
The polymerized acrylic monomers are present in an amount of about
5% to about 95% by weight of the polymer. At least 5% by weight of
the polymerized acrylic monomers have a moiety, like a carboxylic
acid or amide moiety, that render the polymer water dispersible.
The polymer contains about 0.25% to about 20% by weight of
polymerized acrylic monomers having a moiety capable of imparting
water dispersibility. The polymerized acrylic monomer portion of
the polymer also can include 0% up to about 95% by weight of vinyl
monomers, like styrene. The polymerized acrylic monomer portion of
the polymer also can include 0% up to about 3% by weight of
monomers having more than one vinyl group, like divinylbenzene.
The water-dispersible polymer, therefore, has the general
structural formula:
wherein E is the epoxy resin portion of the polymer, L is the
linking portion of the polymer, and A is the polymerized acrylic
portion of the polymer. The polymer is rendered water dispersible
by adding a base, e.g., a fugitive base, to the polymer.
The epoxy portion of the water-dispersible polymer provides
adhesion, and crosslinking capabilities for mar, chemical, and
corrosion resistance. The acrylic portion of the water-dispersible
polymer provides flow, wetting, and hardness properties, and
provides the hydrophilicity that is necessary to disperse the
water-dispersible polymer in water. Linking the epoxy and acrylic
portions provides enhanced flexibility and resistance properties to
the water-dispersible polymer. The water-dispersible polymer,
therefore, exhibits the excellent flexibility and formability
required in a can coating, and exhibits improved chemical
resistance properties.
Components (a) through (c) of the coating composition are dispersed
in an aqueous carrier such that a coating composition includes
about 5% to about 50%, and preferably about 10% to about 50% of
nonvolatile components, by weight of the total composition. Other
optional components, such as a pigment, a filler, or an additive to
enhance composition esthetics or performance, also can be included
in the composition, and accordingly increase the weight percent of
total nonvolatile material in the composition to above about 60% by
weight of the total coating composition. The carrier of the coating
composition also includes a volatile organic solvent to assist in
dispersing or emulsifying composition ingredients or to improve
application of the coating composition to a substrate. A coating
composition typically includes about 15% to about 35% by weight of
a volatile organic solvent.
As used here and hereinafter, the term "coating composition" is
defined as a coating composition including a water-dispersible
polymer, a fugitive base, a curing agent, and any other optional
ingredients dispersed in the carrier. The term "cured coating
composition" is defined as an adherent polymeric coating resulting
from curing a coating composition.
A coating composition, after application to a metal substrate, and
subsequent curing at a sufficient temperature for a sufficient
time, provides an adherent layer of a cured coating composition
that effectively inhibits corrosion; exhibits excellent flexibility
and adhesion to the metal substrate; and does not adversely affect
a product, like a food or beverage, that contacts the cured coating
composition. Because of these advantageous properties, a cured
coating composition can be used to coat the interior of food and
beverage containers and overcome the disadvantages associated with
conventional polyvinyl chloride-based compositions and epoxy-based
compositions. A cured coating composition comprises the
water-dispersible polymer and the curing agent essentially in the
amounts these ingredients are present in the coating composition,
expressed as nonvolatile material. The fugitive base is expelled,
or removed, from a coating composition during the cure cycle.
In accordance with another important aspect of the present
invention, a cured coating composition demonstrates excellent
flexibility, product resistance, and adhesion to a metal substrate
compared to prior epoxy/acrylic resin-based coatings. The excellent
adhesion of a cured coating composition to a metal substrate
improves the corrosion-inhibiting properties of the coating
composition. The excellent flexibility of a cured coating
composition facilitates processing of the coated metal substrate
into a coated metal article, like in molding or stamping process
steps, such that the cured coating composition remains in
continuous and intimate contact with the metal substrate. A cured
coating composition also exhibits excellent chemical resistance, is
sufficiently hard to resist scratching, and does not adversely
affect a food or beverage packaged in a container having an
interior surface coated with the cured coating composition.
In accordance with another important aspect of the present
invention, a coating composition provides a cured coating
composition that overcomes the disadvantages of prior
epoxy/acrylic-based coatings and of conventional polyvinyl
chloride-based coatings used to coat the interior of containers for
food and beverages. In addition, a present coating composition can
be used on both the interior and exterior of can bodies and can
ends, and on closures, thereby obviating the need for a container
manufacturer to use multiple coating compositions.
These and other aspects and advantages of the present invention
will become apparent from the following detailed description of the
preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The coating compositions of the present invention, after curing,
provide cured coating compositions that effectively inhibit the
corrosion of metal substrates, such as, but not limited to,
aluminum, iron, steel and copper. The cured coating compositions,
after curing, also demonstrate excellent adhesion to the metal
substrate; excellent chemical resistance and scratch resistance;
and excellent flexibility.
In general, a coating composition of the present invention
comprises: (a) a water-dispersible polymer, (b) a fugitive base,
and (c) a curing agent in (d) a carrier comprising water and
organic solvents. In addition, the present coating compositions can
include optional ingredients, like lubricants, that improve the
esthetics of the composition, that facilitate processing of the
composition, or that improve a functional property of the
composition. The individual composition ingredients are described
in more detail below.
(a) The Water-Dispersible Polymer
The water-dispersible polymer is prepared from: (i) an epoxy
compound having about two epoxy groups, (ii) a linking compound
having an activated unsaturated carbon-carbon bond moiety and a
moiety capable of reacting with an epoxy group, and (iii) acrylic
monomers, at least a portion of which are capable of rendering the
polymer water dispersible. The linking compound (ii) provides a
covalent link between the epoxy compound (i) and the polymerized
acrylic monomers (iii).
In accordance with an important feature of the present invention,
the water-dispersible polymer is present in the coating composition
in an amount of about 5% to about 60%, and preferably about 10% to
about 50%, by weight of nonvolatile material.
As demonstrated hereafter, the epoxy portion of the
water-dispersible polymer imparts adhesion properties, and chemical
and mar resistance, to a cured coating composition. The acrylic
portion of the water-dispersible polymer provides the functionality
necessary to disperse the polymer in water and also imparts flow,
hardness, and wetting properties. Flexibility and chemical
resistance of the cured coating composition is improved over
previous epoxy/acrylate-based compositions because a
water-dispersible polymer having covalently linked epoxy and
acrylic portions is present in the coating composition. The cured
coating composition exhibits the advantageous properties of a
combination of an epoxy resin and an acrylic resin, with the added
advantage that the epoxy and acrylic portions of the polymer are
covalently linked.
The flexibility of a cured coating composition is an important
feature because the coating composition then can be applied to a
metal substrate, and cured, prior to shaping the metal substrate
into a metal article, such as a can end, a can body, or a closure.
The flexibility imparted to a cured coating composition overcomes
rigidity problems associated with prior epoxy-based compositions.
The chemical and mar resistance of the cured composition are
important properties with respect to resisting scratching of the
cured coating composition during manufacture into a metal article
and to resisting the corrosive effects of materials packaged in the
metal article.
The water-dispersible polymer is prepared from the epoxy compound,
the linking compound, and acrylic monomers. These components are
reacted to provide a water-dispersible polymer having an EEW of
about 360 to about 20,000, and preferably about 1,000 to about
12,000. The water-dispersible polymer has a weight average
molecular weight (M.sub.w) of about 35,000 to about 75,000, and
preferably about 45,000 to about 65,000; and a number average
molecular weight (M.sub.n) of about 6,000 to about 25,000, and
preferably about 7,000 to about 16,000.
The individual components of the water-dispersible polymer are
described in more detail below.
(i) Epoxy Compound Having About Two Epoxy Groups
An epoxy compound having about two epoxy groups is present in an
amount of about 5% to about 95%, and preferably from about 10% to
about 90%, by weight of the water-dispersible polymer. To achieve
the full advantage of the present invention, the epoxy compound is
present in an amount of about 15% to about 85% by weight of the
water-dispersible polymer.
During preparation of the water-dispersible polymer, a portion of
the epoxy groups provided by the epoxy compound are consumed in a
reaction with the linking compound. However, as discussed
hereafter, the epoxy compound, after modification by reaction with
the linking compound, contains at least one epoxy group.
The epoxy compound contains an average of about 1.5 to about 2.5
epoxy groups per molecule of epoxy compound. If the average number
of epoxy groups exceeds about 2.5, excessive crosslinking of the
composition can result in a cured coating that is too hard or
brittle. The epoxy compound has an EEW of about 180 to about
20,000, and preferably about 1,000 to about 12,000. To achieve the
full advantage of the present invention, the epoxy compound has an
EEW of about 2,000 to about 8,500.
The epoxy compound imparts chemical and mar resistance to the cured
coating composition. If the epoxy compound is present in an amount
below about 5% by weight of the water-dispersible polymer, the
cured coating composition is brittle and can form cracks or lose
adhesion during manufacture of a metal article. In addition,
crosslinkable moieties are present in an insufficient amount to
achieve proper cure of coating. If the epoxy-containing compound is
present in an amount above about 95% by weight of the
water-dispersible polymer, the cured coating composition does not
have sufficient flow and wetting properties, and dispersion of the
polymer in water is increasingly difficult. Within the above weight
ranges, the cured coating composition is sufficiently flexible to
permit deformation of a cured coating composition without forming
cracks, and is sufficiently hard to exhibit excellent chemical and
mar resistance.
The epoxy compounds having about two epoxy groups typically is a
linear epoxy resin terminated at each molecular end of the resin
with an epoxy group. The epoxy compounds having about two epoxy
groups, therefore, average about 1.5 to about 2.5 epoxy groups per
molecule of epoxy compound.
The epoxy compound can be an aliphatic epoxy compound or an
aromatic epoxy compound. The preferred epoxy compounds are
aromatic, like epoxy resins based on the diglycidyl ether of
bisphenol A. The epoxy compound has an EEW of about 180 to about
20,000, and preferably about 1,000 to about 12,000. The epoxy
compounds have a weight average molecular weight (M.sub.w) of about
400 to about 50,000. An epoxy compound can be used in its
commercially available form, or can be prepared by advancing a low
molecular weight epoxy compound by standard methods well known to
those skilled in the art, e.g., advancing an epoxy compound having
an EEW of about 180 to about 500 with bisphenol A to produce an
epoxy compound having an EEW of about 1,000 to about 12,000.
Exemplary epoxy compounds include, but are not limited to, DER 664,
DER 667, DER 668, and DER 669, all available from Dow Chemical Co.,
Midland, Mich., and EPON 1004, EPON 1007, and EPON 1009, all
available from Shell Chemical Co., Houston, Tex. An exemplary low
molecular weight epoxy compound that used in its commercial form,
or can be advanced with bisphenol A, is EPON 828, available from
Shell Chemical Co.
In general, suitable epoxy compounds are aliphatic-,
cycoaliphatic-, or aromatic-based epoxy resins, such as, for
example, epoxy resins represented by structural formulae I and II:
##STR1## wherein each A is, independently, a divalent hydrocarbyl
group having 1 to about 12, preferably 1 to about 6, and most
preferably 1 to about 4, carbon atoms; each R is, independently,
hydrogen or an alkyl group having 1 to about 3 carbon atoms; each X
is, independently, hydrogen, a hydrocarbyl or hydrocarbyloxy group
having 1 to about 12, preferably 1 to about 6, and most preferably
1 to about 4, carbon atoms, or a halogen atom, preferably chlorine
or bromine; n is 0 or 1, and n' has an average value of 0 to about
150, and preferably 0 to about 100.
In particular, the preferred epoxy resins are the (diglycidyl
ether/bisphenol-A) resins, i.e., polyether diepoxides prepared by
the polymeric adduction of bisphenol-A (III) ##STR2## and the
diglycidyl ether of bisphenol-A (IV). ##STR3## The diglycidyl ether
can be preformed by reacting two molecules of epichlorohydrin with
one molecule of the bisphenol-A in the presence of a base, such as
sodium hydroxide. Preferably, however, this reaction is carried out
in such a manner that the resulting diglycidyl ether molecules
react in situ with bisphenol molecules to produce the epoxy
resin.
In this case, the epoxy resin is a mixture including polymeric
species corresponding to different values of n' in the following
idealized formula V: ##STR4## wherein n' is a number from 0 to
about 150.
In addition to bisphenol-A, useful epoxy resins can be prepared by
advancing a diglycidyl ether of a bisphenol listed below with an
exemplary, but nonlimiting, bisphenol listed below: ##STR5##
Other epoxy resins that can be used as a component of the
water-dispersible polymer are prepared from the following starting
epoxy-containing materials. These epoxy-containing materials are
reacted with bisphenol-A or another bisphenol to adjust the
molecular weight of the epoxy compound to a sufficiently high
range. ##STR6##
(ii) Linking Compound Having an Activated Unsaturated Carbon-Carbon
Bond Moiety and a Moiety Capable of Reacting with an Epoxy
Group
The linking compound used to prepare a water-dispersible polymer
has two functional groups and covalently links the epoxy portion of
the water-dispersible polymer to the polymerized acrylic monomer
portion of the polymer. The linking compound is present in the
water-dispersible polymer in an amount of about 0.003% to about 4%,
and preferably about 0.003% to about 2.5%, by weight of the
water-dispersible polymer.
In accordance with another important feature of the present
invention, the linking compound is present in a sufficient amount
to react with at least 1% and up to about 50% of the epoxy groups
provided by the epoxy compound. Preferably, the linking compound is
present in a sufficient amount to react with about 5% to about 40%,
and most preferably about 5% to about 25%, of the epoxy groups
provided by the epoxy compound. Accordingly, a reaction between the
epoxy compound and the linking compound does not consume all the
epoxy groups, and sufficient epoxy groups remain such that the
water-dispersible polymer contains at least one epoxy group.
As previously stated, the linking compound is a bifunctional
monomer. One functionality is a moiety capable of reacting with an
epoxy group. The second functionality is a moiety having an
activated unsaturated carbon-carbon bond. As used herein, the term
"activated unsaturated carbon-carbon bond" refers to a
carbon-carbon triple bond, i.e., an acetylenic bond, or to
conjugated carbon-carbon double bonds.
The linking compounds have the general structural formulae VI or
VII ##STR7## wherein R.sub.1 is hydrogen, an aliphatic hydrocarbyl
group, an aliphatic cyclohydrocarbyl group, or an aromatic
hydrocarbyl group; r is a numeral from 1 to 6; s is a numeral from
0 to 6; p is a numeral from 0 to 18; and Y is a moiety capable of
reacting with an epoxy group. Preferably, the linking compound has
a maximum of twelve carbon atoms.
In particular, R.sub.1 can be an aromatic hydrocarbyl group, like
phenyl, or a substituted aromatic hydrocarbyl group, like a C.sub.1
-C.sub.10 alkoxy-substituted phenyl, a halo-substituted phenyl, or
a C.sub.1 -C.sub.18 alkyl-substituted phenyl. As used herein, the
term "halo" includes fluoro, chloro, bromo, and iodo. The R.sub.1
group also can be an aliphatic hydrocarbyl group or an aliphatic
cyclohydrocarbyl group, either substituted or unsubstituted.
Nonlimiting examples of R.sub.1 are hydrogen; a C.sub.1 to C.sub.18
alkyl group, and preferably a C.sub.1-C.sub.10 alkyl group; a
C.sub.5 to C.sub.7 cycloalkyl group; a phenyl-substituted C.sub.1
-C.sub.18 alkyl or C.sub.5 -C.sub.7 cycloalkyl group; and a
halo-substituted alkyl or cycloalkyl group. The R.sub.1 group also
can be an unsaturated C.sub.1 to C.sub.18 aliphatic hydrocarbyl
group or an unsaturated C.sub.5 to C.sub.7 cycloaliphatic
hydrocarbyl group, i.e., the group contains one or more
carbon-carbon double bonds or carbon-carbon triple bonds. Such
unsaturated aliphatic hydrocarbyl and cyclohydrocarbyl groups can
be substituted or unsubstituted. Any substituent groups on R.sub.1
are sufficiently nonreactive such that the substituents do not
interfere in the preparation of the modified epoxy compound or the
water-dispersible polymer. To achieve the full advantage of the
present invention, R.sub.1 is hydrogen, a C.sub.1 -C.sub.4 alkyl
group, a C.sub.5 -C.sub.7 cycloalkyl group, or phenyl.
The identity of the Y group is not limited, except that the Y group
is capable of reacting with an epoxy group. Therefore, the Y group
can be, but is not limited to, carboxyl (--CO.sub.2 H), amido
(--CON(R.sub.2).sub.2), amino (--N(R.sub.2).sub.2), hydroxyl
(--OH), or mercapto (--SR.sub.3), wherein R.sub.2 groups are,
independently, hydrogen, C.sub.1 -C.sub.4 alkyl, or phenyl, and
R.sub.3 is hydrogen, C.sub.1 -C.sub.4 alkyl, or phenyl.
Specific linking compounds include, but are not limited to, sorbic
acid, sorbic alcohol, dicyclopentadiene acids, conjugated
unsaturated fatty acids (e.g., eleostearic acid), 3-pentyn-1-ol,
2-pentyn-1-ol, 4-pentynoic acid, 4-pentyn-1-ol, 4-pentyn-2-ol,
1-pentyn-3-ol, heptacose-10,12-diynoic acid, heptadeca-2,4-diynoic
acid, heneicosa-2,4-diynoic acid, 2-heptynoic acid, 2-hexynoic
acid, nonacosa-10,12-diynoic acid, nonadeca-1,4-diynoic acid,
2-nonynoic acid, pentadeca-2,4-diynoic acid,
pentacosa-10,12-diynoic acid, phenylpropiolic acid, propiolic acid,
tetrolic acid, tricosa-10,12-diynoic acid, 10-undecynoic acid,
1-butyn-3-ol, 2-butyn-1-ol, 3-butyn-1-ol, 2-decyn-1-ol,
3-decyn-1-ol, 3,6-dimethyl-1-heptyn-3-ol,
3,5-dimethyl-1-hexyn-3-ol, 3,4-dimethyl-1-pentyn-3-ol,
3-ethyl-1-heptyn-3-ol, 4-ethyl-1-hexyn-3-ol,
3-ethyl-5-methyl-1-heptyn-3-ol, 4-ethyl-1-octyn-3-ol,
3-ethyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, 1-heptyn-3-ol,
2-heptyn-1-ol, 3-heptyn-1-ol, 4-heptyn-2-ol, 5-heptyn-3-ol,
1-hexyn-3-ol, 2-hexyn-1-ol, 3-hexyn-1-ol, 4-hexyn-2-ol,
5-hexyn-1-ol, 5-hexyn-3-ol, 3-methyl-1-butyn-3-ol,
5-methyl-1-hexyn-3-ol, 3-methyl-1-pentyn-3-ol, 3-nonyn-1-ol,
1-octyn-3-ol, 3-octyn-1-ol, 1-phenyl-2-propyn-1-ol, 2-propyn-1-ol,
10-undecyn-1-ol, 3-aminophenylacetylene, propargylamine, and
mixtures thereof. A preferred linking compound is sorbic acid,
having the structure (VIII).
(iii) Acrylic Monomers
The acrylic monomers, after polymerization, are present in an
amount of about 5% to about 95%, and preferably about 10% to about
90%, by weight of the water-dispersible polymer. To achieve the
full advantage of the present invention, the polymerized acrylic
monomers are present in an amount of about 15% to about 85%, by
weight of the water-dispersible polymer.
The acrylic monomers are polymerized in a free radical
polymerization reaction, in the presence of the linking compound,
to covalently bond the acrylic portion of the water-dispersible
polymer to the linking compound through the activated unsaturated
carbon-carbon bond moiety. Preferably, the acrylic monomers are
polymerized in the presence of the linking compound after the
linking compound has been covalently bound to the epoxy
compound.
In accordance with an important feature of the present invention,
at least a portion of the acrylic monomers are capable of rendering
the polymer dispersible in water. These monomers are defined as
monomers that yield either water-soluble homopolymers or
homopolymers that are rendered water soluble by neutralization with
a base. The acrylic monomers can include 0% up to about 95%, by
total weight of monomers, of vinyl monomers. To avoid excessive
branching, the amount of polyvinyl monomers is 0% to about 3% by
total weight of monomers.
The acrylic monomer typically comprises an
.alpha.,.beta.-unsaturated carboxylic acid. The .alpha.-.beta.
unsaturated carboxylic acid renders the polymer water dispersible
after neutralization with a base. Suitable
.alpha.,.beta.-unsaturated carboxylic acid monomers include, for
example, acrylic acid, methacrylic acid, crotonic acid, itaconic
acid, maleic acid, mesaconic acid, citraconic acid, sorbic acid,
fumaric acid, and mixtures thereof. The acrylic monomer also can
include acrylamide or methacrylamide which can render the polymer
water dispersible.
The .alpha.,.beta.-unsaturated carboxylic acid conventionally is
copolymerized with a vinyl or an acrylic monomer, like styrene or
an acrylic acid ester. Polymerizable vinyl and acrylic monomers
suitable for copolymerization with an .alpha.,.beta.-unsaturated
carboxylic acid include, for example, aromatic and aliphatic
compounds including vinyl moieties and esters and amides of
.alpha.,.beta.-unsaturated carboxylic acids. Nonlimiting examples
of suitable vinyl and acrylic monomers include styrene and
halostyrenes; isoprene; conjugated butadiene;
.alpha.-methylstyrene; vinyl toluene; vinyl naphthalene; the
methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isoamyl,
hexyl, ethylhexyl, lauryl, and other C.sub.4 -C.sub.12 alkyl
acrylates, methacrylates and crotonates; dimethyl maleate, dibutyl
fumarate and similar diesters of .alpha.,.beta.-unsaturated
dicarboxylic acids; and mixtures thereof. Other suitable
polymerizable vinyl monomers include vinyl chloride, acrylonitrile,
methacrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate,
isobutoxymethyl acrylamide, and the like.
The preferred acrylic monomers are methyl acrylate, methyl
methacrylate, ethyl acrylate, butyl acrylate, acrylic acid,
methacrylic acid, and mixtures thereof. A preferred vinyl monomer
is styrene. The most preferred acrylic and vinyl monomers are
styrene, methacrylic acid, acrylic acid, and mixtures thereof.
The acrylic monomers are polymerized and covalently bonded to the
linking compound by subjecting the acrylic monomers and the linking
compound to free radical polymerization conditions known to persons
skilled in the art. Therefore, the acrylic monomers are polymerized
and covalently bonded to the linking compound in the presence of a
free radical initiator. Useful free radical initiators include, but
are not limited to, redox initiators, peroxide-type catalysts,
like, for example, cumene hydroperoxide, or azo compounds, like,
for example, azobisisobutyrontrile.
In general, any free radical initiator can be used in preparing the
water-dispersible polymer. One commonly used, and preferred, free
radical initiator is potassium persulfate. In addition to potassium
persulfate, other useful free radical polymerization catalysts
include, but are not limited to, redox initiators, such as a
sulfite or bisulfite of an alkali metal, ammonium sulfite, ammonium
metabisulfate, ammonium bisulfite, a persulfate of an alkali metal
or ammonium persulfate; a peroxy compound, such as a peroxide or a
peroxy acid, like t-butyl hydroperoxide, di-t-butyl hydroperoxide,
benzoyl hydroperoxide, t-butyl peroxide, lauroyl peroxide, methyl
ethyl ketone peroxide, chlorobenzoyl peroxide, t-butyl perbenzoate,
t-butyl peroxy isopropyl carbonate, and
peroxy-3,3,5-trimethylcyclohexane, or a mixture thereof. Also
useful are free radical thermal initiators such as
azobisisobutyronitrile; 4-t-butylazo-4'-cyanovaleric acid;
4,4'-azobis(4-cyanovaleric acid);
2,2'-azobis(2-amidinopropane)dihydrochloride;
2,2'-azobis(2,4-dimethylvaleronitrile); dimethyl
2,2'-azobisisobutyrate; 2,2'-azodimethyl
bis(2,4-dimethyl-valeronitrile); (1-phenylethyl)azodiphenylmethane;
2,2'-azobis(2-methylbutyronitrile);
1,11-azobis(1-cyclohexanecarbonitrile);
2-(carbamoylazo)-isobutyronitrile;
2,2'-azobis(2,4,4-trimethylpenta-2-phenylazo-2,4-dimethyl-4-methoxy)valero
nitrile; 2,2'-azobis(2-methylpropane);
2,2'-azobis(N,N'dimethyleneisobutyramidine)dihydrochloride;
4,4'-azobis(4-cyanopentanoic acid);
2,2'-azobis(2-methyl-N-[1,1-bis-hydroxymethyl)-2-hydroxyethyl]
propionamide);
2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-ethyl]propionamide);
2,2'-azobis[2-methyl-N(2-hydroxyethyl)propionamide];
2,2'-azobis(isobutyramide) dihydrate, and the like. These types of
initiators, redox, peroxy, and thermal, can be used singly or in a
suitable mixture.
The water-dispersible resin is prepared either by reacting the
linking compound with an epoxy compound or by advancing a low
molecular weight epoxy compound to a desired EEW while
simultaneously reacting the advanced epoxy resin with the linking
compound, followed by polymerizing the acrylic monomer in the
presence of the linking compound bonded to the epoxy compound. The
preferred method simultaneously advances a low molecular weight
epoxy compound while reacting the advanced epoxy compound with the
linking compound.
For purposes of illustrating the preparation of a water-dispersible
polymer, the following experiments and reactions were
performed.
First, the ability of a linking compound to covalently bond to an
epoxy group without disrupting the activated unsaturated
carbon-carbon bond moiety of the linking compound was demonstrated
by reacting 1,2-epoxy-3-phenoxypropane (IX) with sorbic acid (VIII)
to provide compound (X). ##STR8##
In particular, compound (X) was prepared by admixing 74.0 gram (g)
(0.49 equivalents) of compound IX, 55.3 g (0.49 equivalents) of
sorbic acid, 0.006 g (500 ppm) tetraethylammonium bromide (TEAB),
and 20 g methyl ethyl ketone in a reaction flask to form a reaction
mixture. The initial acid number of the reaction mixture was about
184.1. A blanket of nitrogen gas (N.sub.2) was applied over the
reaction mixture, then the reaction mixture was heated to
200.degree. F., and held at 200.degree. F. until the acid number
was reduced to less than one. During the reaction, a second portion
of 0.06 g TEAB as added to the heated reaction mixture. After the
acid number dropped below one, the reaction mixture was cooled, and
the methyl ethyl ketone was stripped from the reaction mixture to
provide compound (X). The structure of compound (X) was confirmed
by nuclear magnetic resonance (NMR) spectroscopy.
In experiments wherein sorbic acid was reacted with an advanced
epoxy resin (e.g., EEW of about 1,000), the reaction mixture often
was too viscous to completely dissolve the advanced epoxy resin and
allow a homogeneous reaction with the sorbic acid. To overcome this
problem, sorbic acid (VIII) and bisphenol-A (III) were admixed with
a low molecular weight epoxy compound, and allowed to react
simultaneously with the epoxy compound. The structure of the
resulting epoxy-sorbate polymer was confirmed by NMR spectroscopy.
The conjugated diene portion of sorbic acid was not effected during
the reaction. The sorbate-modified epoxy compound, therefore, has
the structure (XI). ##STR9## wherein t is 0 to about about 70. The
sorbate-modified epoxy compound (XI), therefore, has epoxy groups
available for reaction with a crosslinking agent and an activated
unsaturated carbon-carbon bond moiety available for reaction with
the acrylic monomers.
In other embodiments, the epoxy ring remaining in sorbate-modified
epoxy compound (XI) is opened prior to reacting the
sorbate-modified epoxy compound with the acrylic monomers. For
example, the epoxy ring in compound (XI) can be hydrolyzed to
provide the corresponding .alpha.-glycol compound, wherein the
epoxy ring at the terminal end of the sorbate-modified epoxy
compound is converted to structure (XII). ##STR10##
Similarly, the epoxy ring of compound (XI) can be opened with a
nitrogen compound having the structure (R.sub.4).sub.2 NH, wherein
the R.sub.4 groups are, independently, hydrogen, phenyl, or an
alkyl or hydroxyalkyl group having one to six carbon atoms.
Examples of such nitrogen compounds are ammonia, a primary amine,
or a secondary amine. Opening the epoxy ring with a nitrogen
compound provides an .alpha.-aminoalcohol at a terminal end of the
modified epoxy compound (XI).
In addition, the epoxy ring of a modified epoxy compound can be
opened with a hydroxyl-containing compound having the structure
R.sub.5 OH, wherein R.sub.5 is an alkyl group or a hydroxyalkyl
group having one to six carbon atoms, or R.sub.5 is phenyl. Opening
the epoxy ring with an alcohol provides an .alpha.-hydroxy ether at
a terminal end of the modified epoxy compound.
Furthermore, the epoxy ring of the modified epoxy compound can be
opened with phosphoric acid having the structure (XIII), ##STR11##
wherein the R.sub.6 groups are, independently, hydrogen, an alkyl
group or a hydroxyalkyl group having one to six carbon atoms, or
phenyl. Opening the epoxy ring with a phosphoric acid of structure
(XIII) provides an .alpha.-hydroxy phosphate ester having the
structure (XIV) ##STR12## at the terminal end of the modified epoxy
compound (XI).
To demonstrate that the linking compound copolymerizes with the
acrylic monomers, sorbic acid was reacted with acrylic monomers and
vinyl monomers under free radical polymerization conditions. The
conjugated diene moiety of sorbic acid was not observed in the
resulting polymer. In particular, the following example
demonstrates the copolymerization of sorbic acid, acrylic monomers,
and vinyl monomers.
______________________________________ Ingredient Amount (wt)
______________________________________ (a) Butyl Cellosolve 316 g
(b) n-Butyl Alcohol 96 g (c) Styrene 5.1 g (d) Ethyl Acrylate 113.4
g (e) Methyl Methacrylate 33.9 g (f) Acrylic Acid 21.3 g (g)
Methacrylic Acid 25.5 g (h) Sorbic Acid 3 g (i)
2,2'-Azobisisobutyronitrile 3 g (j) Butyl Cellosolve 50 g (k)
2,2'-Azobisisobutyronitrile 1.3 g (l) 2,2'-Azobisisobutyronitrile
1.3 g (m) 2,2'-Azobisisobutyronitrile 1.3 g
______________________________________
Ingredients (a) and (b) were charged into a reaction flask and
heated to 230.degree. F. Ingredients (c) through (i) were premixed,
then added dropwise to the heated mixture of (a) and (b) over a
90-minute period, with agitation and while maintaining a
temperature of 230.degree.-235.degree. F. Residual amounts of the
monomer premix (c)-(i) were washed into the reaction flash with
ingredient (j). The resulting reaction mixture was held at
230.degree. F. for 30 minutes, then ingredient (k) was added. After
another 30-minute hold at 230.degree. F., ingredient (l) was added.
After a third 30-minute hold at 230.degree. F., ingredient (m) was
added. The reaction mixture then was held at 230.degree. F. for an
additional 60 minutes, then allowed to cool.
The solvents were evaporated from the reaction mixture, and the
resulting copolymer was assayed by NMR for the presence of the
sorbic acid diene moiety. No evidence of a diene moiety was
observed.
As illustrated hereafter, a sorbate-modified epoxy compound of
structural formula (XI) was reacted with acrylic and vinyl monomers
to provide a water-dispersible polymer. The resulting
water-dispersible polymer had the structure:
wherein E is the epoxy portion of the polymer, A is the acrylic
portion, and L is the linking portion which covalently links E to
A.
(b) The Fugitive Base
The water-dispersible polymer contains a sufficient amount of
acrylic monomers capable of rendering the polymer dispersible in
water. These acrylic monomers typically are
.alpha.,.beta.-unsaturated carboxylic acids and these monomers
render the polymer water dispersible by neutralizing the carboxylic
acid moiety with a fugitive base.
A fugitive base is included in a sufficient amount such that about
20% to about 100% of the carboxylic acid groups of the acrylic
portion of the water-dispersible monomer are neutralized. An excess
amount of fugitive base does not adversely affect the coating
composition, but the excess amount of fugitive base provides no
advantages and, therefore, is wasted. A fugitive base preferably is
present in an amount sufficient to neutralize at least about 35% to
about 75% of the carboxylic acid groups present in a water-borne
coating composition. The precise amount of fugitive base added to
the composition is determined from the acid number of the
water-dispersible polymer and from the basicity of fugitive
base.
A fugitive base is a relatively volatile compound that is expelled
from a coating composition during cure. Accordingly, a coating
composition, during cure, reverts to a more water insoluble form
and, therefore, provides a cured coating composition that exhibits
excellent chemical resistance and excellent blush resistance.
A fugitive base usually is a primary, secondary or tertiary amine,
either aromatic or aliphatic, or a primary, secondary or tertiary
alkanolamine, or ammonium, an alkylammonium hydroxide, or an
arylammonium hydroxide, or mixtures thereof. Nonlimiting examples
of a fugitive base include ammonium hydroxide, a tetraalkylammonium
hydroxide, wherein an alkyl group has one to about 4 carbon atoms
(e.g., tetramethylammonium hydroxide), monoethanolamine,
dimethylamine, methyldiethanolamine, benzylamine, diisopropylamine,
methylethanolamine, butylamine, piperazine, dimethylethanolamine,
diethylethanolamine, diethanolamine, morpholine,
N-methylmorpholine, N-ethylmorpholine, triethylamine,
2-dimethylamine-2-methyl-1-propanol, diisopropanolamine,
trimethylamine, N-methylpiperidine, 2-amino-2-methyl-1-propanol,
piperidine, pyridine, dimethylaniline, and similar amines and
alkanolamines, and mixtures thereof.
(c) The Curing Agent
A coating composition of the present invention also includes a
curing agent, such as a phenolic resin or an aminoplast. The
coating composition contains about 0.5% to about 25%, and
preferably about it to about 20%, by weight of nonvolatile material
of the curing agent. To achieve the full advantage of the present
invention, the coating composition contains about it to about 10%,
by weight, of a curing agent.
The curing agent can be a phenolic resin, an aminoplast, a
carbodiimide, or a similar curing agent. The phenolic resin is a
condensation product resulting from a reaction between a phenol and
formaldehyde, and has a low weight average molecular weight of
about 800 to about 8,000, and preferably about 1,200 to about
5,000. Phenol or essentially any other compound including a
hydroxyphenyl moiety can be used as the phenol component of the
phenolic resin. Nonlimiting examples of suitable phenol compounds
include phenol, cresylic acid and bisphenol A. Bisphenol A is the
preferred phenol component of the phenolic resin.
Similarly, an aminoplast can be used as the curing agent. An
aminoplast generally is a low molecular weight partially or fully
alkylated condensation product, like urea-formaldehyde,
melamine-formaldehyde, and benzoguanamine-formaldehyde resins.
Commercially available aminoplasts include, for example, CYMEL 301,
CYMEL 303, CYMEL 370, and CYMEL 373, all being melamine-based and
commercially available from American Cyanamid, Stamford, Conn.,
e.g., CYMEL 301 is hexamethoxymethyl melamine.
Other examples of aminoplast resins are of the type produced by the
reaction of aldehyde and formoguanamine, ammeline,
2-chloro-4,6-diamine-1,3,5'triazine;
2-phenyl-p-oxy-4,6-diamino-1,3,5-triazine; and
2,4,6-triethyl-triamino-1,3,5-triazine. The mono-, di, or triaryl
melamines, for instance, 2,4,6-triphenyltriamine-1,3,5-triazine,
are preferred. Other aldehydes used to react with the amino
compound to form the resinous material are crotonic aldehyde,
acrolein, or compounds which generate aldehydes, such as
hexamethylene-tetramine, paraldehyde, and the like.
(d) The Carrier
The carrier of a present coating composition is water based, but
also can include a volatile organic solvent. In general, the
volatile organic solvents included in the coating composition have
sufficient volatility to evaporate essentially entirely from the
coating composition during the curing process, such as during
heating at about 350.degree. F. to about 500.degree. F. for about 6
seconds to about 15 minutes.
The volatile organic solvents are included as a portion of the
carrier to help dissolve, disperse and emulsify composition
ingredients, and thereby provide a more stable composition. The
volatile organic solvents also are included to improve the physical
properties of the composition, like surface tension, flow out
during the bake and viscosity, and thereby provide a composition
that is easier to apply and that provides a more uniform cured
coating. The volatile organic solvents improve the flow properties
of a coating composition and facilitates spraying of a coating
composition.
Numerous volatile organic solvents can be included in a present
coating composition. Suitable volatile organic solvents have a
sufficiently low vapor pressure to resist evaporation during
storage and a sufficiently high vapor pressure to be evaporated
from the coating composition during cure. Exemplary, nonlimiting
volatile organic solvents include, but are not limited to, the
methyl, ethyl, propyl, butyl, hexyl or phenyl ether of ethylene
glycol, diethylene glycol, triethylene glycol, propylene glycol or
dipropylene glycol; ethylene glycol methyl ether acetate; ethylene
glycol ethyl ether acetate; ethylene glycol butyl ether acetate;
diethylene glycol ethyl ether acetate; diethylene glycol butyl
ether acetate; propylene glycol methyl ether acetate; dipropylene
glycol methyl ether acetate; n-butanol; hexyl alcohol; hexyl
acetate; methyl n-amyl ketone; butylene glycol; propylene glycol;
diisobutyl ketone; methyl propyl ketone; methyl ethyl ketone;
methyl isobutyl ketone; 2-ethoxyethyl acetate; t-butyl alcohol;
amyl alcohol; 2-ethylhexyl alcohol; cyclohexanol; isopropyl
alcohol; and similar organic solvents, and mixtures thereof.
A preferred volatile organic solvent is n- butanol because coating
composition components are easily dispersed in n-butanol. Another
preferred volatile organic solvent is ethylene glycol monobutyl
ether, i.e., butyl cellosolve.
The carrier also can include a relatively low amount of a nonpolar
organic solvent, such as up to about 10% by weight of the carrier,
without adversely affecting a coating composition, either prior to
or after curing. Exemplary nonpolar organic solvents include a
chlorinated hydrocarbon, an aliphatic hydrocarbon, or an aromatic
hydrocarbon, like toluene, ethylbenzene, benzene, xylene, mineral
spirits, kerosene, naphtha, heptane, hexane, and combinations
thereof.
The amount of carrier included in the coating composition is
limited only by the desired, or necessary, Theological properties
of a coating composition. Usually, a sufficient amount of carrier
is included in a coating composition to provide a composition that
can be processed easily, that can be applied to a metal substrate
easily and uniformly, and that is sufficiently evaporated from a
coating composition during cure within the desired cure time.
A carrier, therefore, is included in the composition in a
sufficient amount to provide a coating composition including about
5% to about 60%, and preferably about 10% to about 50%, by weight
of the nonvolatile material. To achieve the full advantage of the
present invention, a waterborne coating composition includes about
15% to about 45% by weight of the nonvolatile material. The
addition of optional fillers can increase the amount of nonvolatile
material above about 60%.
Therefore, essentially any carrier comprising a major portion of
water and a minor portion of volatile organic solvents is useful in
the present coating composition as long as the carrier adequately
disperses, emulsifies and/or solubilizes the composition
components; is inert with respect to interacting with composition
components and thereby adversely affecting the stability of the
coating composition or the ability of the coating composition to
effectively cure; and evaporates quickly, essentially entirely and
relatively rapidly to provide a cured coating composition that
inhibits the corrosion of a metal substrate, that does not
adversely affect a food or beverage that contacts the cured coating
composition, and that demonstrates sufficient physical properties,
like adhesion and flexibility, for use as a coating on the interior
or exterior of a container or a closure.
(e) Other Optional Ingredients
A coating composition of the present invention also can include
other optional ingredients that do not adversely affect the coating
composition or a cured coating composition resulting therefrom.
Such optional ingredients are known in the art, and are included in
a coating composition to enhance composition esthetics; to
facilitate manufacturing, processing, handling, and application of
the composition; and to further improve a particular functional
property of a coating composition or a cured coating composition
resulting therefrom.
Such optional ingredients include, for example, dyes, pigments,
extenders, fillers, additional anticorrosion agents, flow control
agents, thixotropic agents, dispersing agents, antioxidants,
adhesion promoters light stabilizers, and mixtures thereof. A
nonionic or an anionic surfactant is included in a coating
composition to improve flow properties. A wax emulsion and/or
dispersion of a synthetic lubricant is included to improve the slip
properties of a cured coating composition. Each optional ingredient
is included in a sufficient amount to serve its intended purpose,
but not in such an amount to adversely affect a coating composition
or a cured coating composition resulting therefrom.
A coating composition of the present invention is prepared by first
preparing the water-dispersible polymer. The water-dispersible
polymer preferably is prepared by simultaneously advancing the
epoxy compound and reacting the epoxy compound with the linking
compound. The resulting modified epoxy compound is reacted with
acrylic monomers under free radical polymerization conditions to
provide the water-dispersible polymer.
The water-dispersible polymer then is admixed with the fugitive
base, curing agent, and carrier, i.e., water and volatile organic
solvent. The carrier is present in a sufficient amount to adjust
the amount of nonvolatile material in the coating composition to a
predetermined level. Optional ingredients can be added to the
coating composition either prior to or after the addition of the
carrier.
To demonstrate a coating composition of the present invention, the
following Examples and Comparative Examples were prepared, then
applied to a metal substrate, and finally cured to provide a coated
metal substrate. The coated metal substrates then were tested,
comparatively, for use as a food or beverage container. The cured
coatings were tested for an ability to inhibit corrosion of a metal
substrate; for adhesion to the metal substrate; for chemical
resistance; for flexibility; and for scratch and mar resistance. A
composition of the present invention was compared to a commercial
vinyl organosol composition (i.e., Comparative Example 1) that is
widely used in coating metal substrates for food and beverage
applications.
______________________________________ Comparative Example 1
Commercial Vinyl Organosol Composition % % (by Ingredient (by
weight) weight NVM.sup.1) ______________________________________
Xylene 29.45 -- Diisobutyl Ketone 13.77 -- Diacetone Alcohol 20.90
-- Solution Vinyl .sup.2 11.61 34.32 Phenolic Resin .sup.3 2.02
2.99 Epoxy Resin .sup.4 1.01 2.99 Lubricant .sup.5 1.31 0.77 Vinyl
Cloride Dispersion 19.93 58.92 Resin.sup.6
______________________________________ .sup.1 NVM is nonvolatile
material; .sup.2 UCAR Solution Vinyl VMCC, available as a 100%
active material, from Union Carbide Corp., Danbury, CT; .sup.3 50%
nonvolatile material; .sup.4 EPON 828, available as a 100% active
material, from Shell Chemica Co., Houston, TX; .sup.5 POLYSPERSE
.RTM., 20% active material; and .sup.6 OXY 1730, available as a
100% active material, from Occidental Chemical Co., Houston,
TX.
The composition of Comparative Example 1 contains about 33.8%
nonvolatile material.
______________________________________ EXAMPLE 1 % (by Ingredient %
(by weight) weight NVM.sup.1)
______________________________________ Water-Dispersible 91.46 97.0
Polymer/Fugitive Base Solution.sup.7 Curing Agent .sup.8 1.52 2.3
Lubricant .sup.9 0.92 0.7 N-Butyl Alcohol 1.22 Deionized Water 4.88
______________________________________ .sup.7 Aqueous solution of
waterdispersible polymer solubilized with dimethylethanolamine, 35%
solids content, see Example 2; .sup.8 Phenolic resin, based on
phenol and paraformaldehyde, 50% active; and .sup.9 MICHEM 160,
Michelman Chemical Inc., Cincinnati, OH, a 25% active emulsion of
carnauba wax.
The composition of Example 1 is a coating composition of the
present invention containing about 33% nonvolatile material. The
composition of Example 1 is prepared by simply admixing composition
ingredients until homogeneous. The composition of Example 1 is
based on the water-dispersible polymer prepared as set forth below
in Example 2.
EXAMPLE 2
Water-Dispersible Polymer/Fugitive Base Solution
An epoxy compound, i.e., EPON 828, a diglycidylether of
bisphenol-A, (EEW 187, 180 pounds) was added to a
nitrogen-blanketed reactor fitted with a reflux condenser. The
epoxy compound was heated to about 170.degree. F. to about
175.degree. F., then a sufficient amount of bisphenol-A was added
to the heated epoxy compound to provide an epoxy resin of EEW of
about 3000 (e.g., about 99 pounds). In addition, 464 grams (g) of
sorbic acid and 77 g of a phosphonium salt catalyst (i.e., SHELL
Catalyst 1201, available from Shell Chemical Co., Houston, Tex.)
were added to the reactor.
The resulting mixture was heated to 240.degree. F. while
maintaining a nitrogen blanket. After reaching 240.degree. F., the
mixture was allowed to cool to 100.degree. F. An exothermic
reaction raised the temperature to 270.degree. F., and the
temperature then was allowed to raise at the rate of about one to
about one and one-half Fahrenheit degrees per minute by cooling the
mixture until the temperature reached about 350.degree. F. (peak
temperature was about 365.degree. F.). After the exotherm subsided,
the mixture was held at about 350.degree. F. to about 360.degree.
F., by heating, for about one hour. When the epoxy resin attained
an EEW of greater than about 3000, butyl cellosolve (176 pounds)
was added to the mixture, and the mixture was allowed to cool to
about 250.degree. F.
Then, n-butyl alcohol (32.8 pounds) was added to the mixture, and
the resulting mixture was further cooled to 230.degree. F. A premix
of styrene (790 g), ethyl acrylate (38.7 pounds), methyl
methacrylate (11.6 pounds), acrylic acid (3,299 g), and methacrylic
acid (3,950 g), and having an acid number of about 166, was
prepared. Azobisisobutyronitrile initiator (464 g) was added to the
monomer premix, then the resulting acrylic monomer/initiator
mixture was added to the reactor over a 90-minute time period,
while maintaining a temperature of about 230.degree. F. Residual
amounts of acrylic monomers were flushed into the reaction vessel
with 14.4 pounds of butyl cellosolve and held at about 230.degree.
F. for an additional 30 minutes.
Next, a premix of 201 g of azobisisobutyronitrile and 402 g of
butyl cellosolve was added to the reactor, and the resulting
mixture was held for an additional 30 minutes at about 230.degree.
F. This procedure was repeated two additional times to ensure that
the acrylic monomers were polymerized.
The contents of the reactor then were cooled to about 220.degree.
F., followed by the addition of 4090 g of deionized water. The
contents of the reactor were cooled to 212.degree. F., then a
premix of water (4090 g) and dimethylethanolamine (4090 g) was
added to the reactor. After a 10-minute hold, heated deionized
water (262 pounds, 200.degree. F.) was added to the reactor over a
one-hour time period. The reaction product was allowed to cool to
about 195.degree. F. to about 200.degree. F. during the water
addition. Next, deionized water (135 pounds) was quickly added to
cool the reaction product to about 105.degree. F. The reaction
product then was adjusted to the desired solids content by the
addition of deionized water.
The polymer solution of Example 2 had a solids content of about
35%, by weight; a pH of about 7.25; a viscosity of 350 cps
(centipoise) measured on a #3 spindle at 25.degree. C. and 20 rpm;
an acid number on solids of about 32.5, and a base number on solids
of about 16.2. The water-dispersible polymer/fugitive base solution
of Example 2 was used as the major component of the composition of
Example 1.
The composition of Example 1 was applied to both sides of an
aluminum substrate at a rate to provide about 5.2 to about 7
milligrams per square inch (msi) interior dry film weight and about
2.3 to about 2.8 msi exterior dry film weight. The composition of
Example 1 was applied at a rate of about 150 feet per minute, and
was cured at about 450.degree. F. for about 11 seconds. The
composition of Example 1 was easy to apply, exhibiting excellent
flow, no foaming, no skinning, no significant solvent loss, and no
apparent rise in viscosity after two hours. The cured coating
composition exhibited excellent gloss.
The composition of Example 1 was compared to the composition of
Comparative Example 2. Comparative Example 1 was used as a control.
The composition of Comparative Example 2 was similar to the
composition of Example 1, except sorbic acid was omitted from the
composition of Example 2. The composition of Comparative Example 2,
therefore, does not include a linking compound to covalently bond
the epoxy portion of the polymer to the polymerized acrylic portion
of the polymer.
In summary, Comparative Example 2 contains 97%, by weight of
nonvolatile material, of an epoxy-acrylic dispersion. The
epoxy-acrylic dispersion contains 33% nonvolatile material, and is
based on an advanced epoxy resin, styrene, ethyl acrylate, methyl
methacrylate, and methacrylic acid. The epoxy-acrylic dispersion of
Comparative Example 2 is prepared in an essentially identical
manner as Example 2, except that sorbic acid is omitted and the
epoxy resin used in Comparative Example 2 is advanced prior to the
synthesis, rather than as a first step of the synthesis. The
composition of Comparative Example 2 contains the same curing agent
and lubricant, in the same amounts, as Example 1; and contains 30%
nonvolatile material.
The compositions of Example 1 and Comparative Examples 1 and 2 were
applied to a metal substrate (e.g., an aluminum substrate), and
then cured to provide a coated metal substrate. The coated metal
substrates then were tested, comparatively, for use as the interior
surface of a food or beverage container. As will be demonstrated
more fully hereinafter, a cured coating composition resulting from
curing a coating composition of the present invention is suitable
as the interior or exterior coating of a metal container for food
or beverages, or for a closure.
In particular, a coating composition of the present invention is
applied to a metal substrate, then cured for a sufficient time at a
sufficient temperature, such as for about 3 to about 5 minutes at
about 350.degree. F. to about 500.degree. F., to provide an
adherent cured coating composition on the metal substrate. The
coated metal substrate then is shaped into a container or other
metal article.
Therefore, the compositions of Example 1 and Comparative Examples 1
and 2 were individually applied to a clean, untreated aluminum
substrate in a sufficient amount to provide a cured film thickness
of about 0.1 mil. Each composition was reduced to a solids content
of about 28% by weight with deionized water before applying the
composition to the metal substrate. After individually applying a
composition of Example 1 or a composition of Comparative Examples 1
and 2 to an aluminum substrate, the composition was cured through
an HVHT coil oven at 450.degree. F. for about 16 seconds. Each of
the cured coating compositions had a smooth, glossy appearance and
was defect free.
Table I summarizes the results of different tests performed on the
cured coating compositions. TABLE I
TABLE I ______________________________________ Comparative Tests
Film Pencil DOW Composition Weight.sup.1 Hardness WF.sup.2
WP(B,A).sup.3 (B/A) ______________________________________ Example
1 7.3 2H-3H 0.3, 0.3 100/100 80/100 Comparative 7.3 2H-3H 0.3, 0.5
100/100 100/100 Ex. 2 Comparative 7.2 2H 0, 0 100/100 60/100 Ex. 1
(control) ______________________________________ .sup.1 In
milligrams per square inch of substrate; .sup.2 A wet feathering
(WF) test, the coated panels, after immersion in 150.degree. F.
water for 15 minutes, were tested for an ability to resist forming
torn or protruding edges when a tab of the coated metal substrate
is removed from the coated metal substrate, the test simulates
removal of a tab from an easyopen aluminum can, 0 (best results) 5
(worst results); .sup.3 B/A is blush/adhesion, 100excellent,
90good, 0total loss, Wp is we pasteurization, the coated substrate
is tested after immersion in 180.degree. F. water for 30 minutes.
Dow refers to a standard test wherei the coated substrate is tested
by immersing the coated aluminum substrate in a boiling aqueous
solution including 1 weight % Dowfax 2A1 (an anionic surfactant)
for 15 minutes, then testing for blush and adhesion.
The results summarized in Table I show that the composition of
Example 1 has a better blush resistance than a presently used
commercial composition (Comparative Example 1).
The compositions of Example 1 and Comparative Example 2 also were
tested for process resistance. In these tests, liquids are placed
in contact with the coated substrate for a predetermined period of
time under different conditions, then the substrates are tested for
resistance to the effects of these various liquids in an enamel
rating test.
The enamel rating tests the continuity of a cured coating film
applied to a can part, such as a can end or a can body. A can end
or can body is formed after the metal substrate is coated.
Therefore, the cured coating has been deformed during this
manufacturing step. The data presented in Table II show that the
enamel rating for a composition of the present invention (Example
1) is substantially better than the enamel rating of Comparative
Example 2.
The enamel rating test measures the passage of current from an
electrode through an electrolyte to the formed can part. The
coating functions as an insulator, and, accordingly, no current
flows if film continuity is perfect. The lower the milliamp
reading, the more continuous the coating on the metal substrate.
The data in Table II shows a relatively low milliamp reading for
can parts coated with the composition of Example 1, therefore,
showing good film continuity. The composition of Example 1 showed
substantially better process resistance because of a better enamel
rating.
TABLE II ______________________________________ Comparative Testing
Comparative Test.sup.1 Example 1 Example 2
______________________________________ Coated substrate 0.39 .+-.
0.29 1.68 .+-. 0.91 (as made) After 5 minutes in 4.75 .+-. 1.76
10.62 .+-. 2.61 boiling Dowfax 2A1 3 days @ 120.degree. F. 2.49
.+-. 1.25 6.65 .+-. 2.16 Diet Coke 7 days @ 100.degree. F. -- 5.0
.+-. 2.53 Diet Coke 3 days @ 120.degree. F. 1.70 .+-. 0.97 4.48
.+-. 1.43 Diet Sprite ______________________________________ .sup.1
All tests are enamel ratings, in milliamps. Tests were performed
after subjecting a coated substrate to the indicated
conditions.
In general, the composition of Example 1 demonstrates improved
flexibility, adhesion, and enamel rating over the composition of
Comparative Example 2. Example 1 also exhibited properties
comparable to the presently used commercial vinyl organosol
composition of Comparative Example 1. In addition, the compositions
of the present invention exhibit an improved solids/viscosity
relationship permitting the formulation of a high solids
composition having an acceptable viscosity for handling and
application. The present coating compositions, therefore, have
exhibited coating properties at least equal to current commercial
compositions for similar end uses.
The data summarized in Tables I and II illustrate that a coating
composition of the present invention provides a cured coating
composition useful as the interior or exterior coating of a food or
beverage container, or a closure for a food product container. The
present compositions demonstrate excellent blush resistance and
excellent adhesion. The blush resistance test demonstrates the
ability of a cured coating to resist attack by a hot detergent
solution and other liquids. A coating composition for a metal
container must demonstrate excellent adhesion and flexibility
because metal containers are manufactured by first coating flat
sheets of the metal substrate, then forming the coated sheets into
a desired shape. Coatings having poor adhesion properties can
separate from the metal substrate during the shaping process. A
lack of adhesion, therefore, can adversely affect the ability of
the cured coating composition to inhibit corrosion of the metal
substrate. A present coating composition exhibits an excellent
adhesion to a metal substrate, and, therefore, the coating
composition can be applied to a metal substrate, cured, and the
metal substrate subsequently can be deformed without adversely
affecting continuity of the coating film.
The present coating compositions also provided a cured coating
composition having excellent flexibility. Flexibility is an
important property of a cured polymeric coating because the metal
substrate is coated prior to stamping or otherwise shaping the
metal substrate into a desired metal article, such as a metal
container. The coated metal substrate undergoes severe deformations
during the shaping process, and if a coating lacks sufficient
flexibility, the coating can form cracks or fractures. Such cracks
result in corrosion of the metal substrate because the aqueous
contents of the container have greater access to the metal
substrate. Metal substrates coated with a present coating
composition were deformed into the shape of a metal can. No cracks
or fractures were observed. In addition, as previously described, a
cured coating provided by a coating composition of the present
invention is sufficiently adherent to the metal substrate, and
remains sufficiently adherent during processing into a metal
article, and, therefore, further enhances corrosion inhibition.
The comparative tests illustrated in Tables I and II demonstrate
that a cured coating composition of the present invention maintains
adhesion to the metal substrate; is flexible; is sufficiently hard
and, therefore, is scratch and mar resistant; resists blush; and
resists chemical attack.
As an added advantage, a composition of the present invention can
be cured over a relatively wide temperature range of about
350.degree. F. to about 500.degree. F., and over relatively wide
time period of about 3 minutes to about 5 minutes, without
adversely affecting the advantageous physical and chemical
properties of the cured coating composition. A container
manufacturer, therefore, does not have to design the coating
process around the curing characteristics of the coating
composition; nor does the coating manufacturer have to tailor the
curing characteristics of the coating composition to a particular
coating process. The present coating composition, therefore, has a
more universal range of applications. Furthermore, the wide curing
range and the chemical and physical properties demonstrated by the
present coating compositions makes a waterborne coating composition
useful for both the exterior and interior of can bodies and can
ends. Conventionally, different coating compositions are used for
the can body and can end, and for the exterior and interior of the
container. This further expands the range of applications for the
present composition.
Obviously, many modifications and variations of the invention as
hereinbefore set forth can be made without departing from the
spirit and scope thereof and, therefore, only such limitations
should be imposed as are indicated by the appended claims.
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